DTOF camera calibration system and method based on controllable delay optical fiber

Abstract

The invention relates to a DTOF camera calibration system and method based on a controllable delay optical fiber, and the system comprises a delay optical fiber switching module which comprises an optical fiber switcher, a transmitting optical fiber and a receiving optical fiber, the transmitting optical fiber is connected with the transmitting end of a DTOF camera, the receiving optical fiber comprises a plurality of optical fiber branches with different lengths, and the optical fiber branches are connected with the receiving end of the DTOF camera; the optical fiber switcher is used for switchably branching any one of the transmitting optical fiber and the receiving optical fiber to form an optical path; the laser intensity calibration module is arranged on the transmitting optical fiber and is used for dynamically modulating the laser intensity of the DTOF camera; the temperature calibration module is arranged at the transmitting end and the receiving end and is used for performing temperature calibration on the DTOF camera; and the control module is respectively connected with the optical fiber switcher, the laser intensity calibration module and the temperature calibration module, and is used for controlling each calibration module to form a multi-mode calibration environment. According to the invention, the calibration process of the DTOF camera is simplified, and the calibration precision and flexibility are improved.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement technologies, and in particular, to a DTOF camera calibration system and method based on a controllable delay optical fiber. Background Art

[0002] DTOF (Distributed Time-Of-Flight) is a measurement technology based on the time-of-flight principle, which can be used to measure the three-dimensional shape or distance information of an object in space. The DTOF technology has the advantages of non-contact measurement, fast measurement speed, high accuracy, etc., and is widely used in industrial automation, robot navigation, medical imaging and other fields. The basic principle of a DTOF camera is that a transmitting end (TX) emits a laser pulse, the laser pulse propagates in space and is reflected back after encountering an object, and a receiving end (RX) receives the reflected laser pulse, and calculates the distance between the object and the measurement system by measuring the time-of-flight (TOF) of the laser pulse. By scanning the entire measurement area, the DTOF camera can obtain the three-dimensional shape or distance information of the object.

[0003] However, the performance of a DTOF camera is affected by various factors, including the performance of the transmitting and receiving ends, the stability of the optical path, environmental noise, etc. In order to ensure the accuracy and reliability of the DTOF camera, it needs to be calibrated. Calibration refers to determining the parameters and performance of the measurement system through a series of experiments with known conditions, so as to perform correction and calibration in actual measurement.

[0004] Currently, the calibration methods of DTOF cameras mainly have the following deficiencies: (1) The calibration process is complex: Traditional DTOF calibration methods require multiple calibration devices and steps, with cumbersome operations and long time consumption, which is not conducive to rapid deployment and on-site application.

[0005] (2) The calibration accuracy is limited: Due to the limitations of calibration devices and methods, traditional DTOF camera calibration methods often have difficulty achieving high calibration accuracy, which affects the performance of the measurement system.

[0006] (3) Lack of flexibility: Traditional DTOF camera calibration methods are usually targeted at specific measurement scenarios and device configurations, lacking universality and flexibility, and it is difficult to adapt to different measurement requirements and environmental changes. Summary of the Invention

[0007] (1) Technical Problems to be Solved In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a DTOF camera calibration system and method based on a controllable delay optical fiber, aiming to simplify the calibration process of the DTOF camera, improve the calibration accuracy and flexibility.

[0008] (2) Technical Solution To achieve the above object, the main technical solutions adopted by the present invention include: In a first aspect, an embodiment of the present invention provides a DTOF camera calibration system based on a controllable delay optical fiber, including: A delay optical fiber switching module, including an optical fiber switch and a transmitting optical fiber and a receiving optical fiber arranged on both sides of the optical fiber switch. The transmitting optical fiber is connected to the transmitting end of the DTOF camera. The receiving optical fiber includes at least two optical fiber branches with different lengths and is connected to the receiving end of the DTOF camera. The optical fiber switch is configured to switchably form an optical path between the transmitting optical fiber and any one of the optical fiber branches in the receiving optical fiber; A laser intensity calibration module, arranged on the transmitting optical fiber, for applying a modulation voltage to change the transmission characteristics of the laser transmitted in the transmitting optical fiber, so as to dynamically modulate the laser intensity of the DTOF camera; A temperature calibration module, arranged at the transmitting end and the receiving end, for changing the ambient temperature at the transmitting end and the receiving end, so as to perform temperature calibration on the DTOF camera; A control module, respectively connected to the optical fiber switch, the laser intensity calibration module and the temperature calibration module, for controlling the optical fiber switch, the laser intensity calibration module and the temperature calibration module to form a multi-modal calibration environment.

[0009] Optionally, the receiving optical fiber includes at least two optical fiber branches with a length difference of which is positively correlated with the set target delay amount; An optical fiber interface is arranged at the end of the optical fiber branch, and the optical fiber interface is used for pluggable connection with the receiving end.

[0010] Optionally, the transmitting end includes: a laser light source and a first collimating mirror; The laser light source is used to generate transmitted laser; The first collimating mirror is connected to the transmitting optical fiber and is used to collimate the transmitted laser into the transmitting optical fiber.

[0011] Optionally, the receiving end includes: a second collimating mirror, a ground glass and a receiving lens; The second collimating mirror is connected to the receiving optical fiber and is used to collimate the laser transmitted in the receiving optical fiber into parallel laser; The ground glass is used to scatter the parallel laser into a uniformly distributed spot signal; The receiving lens is used to receive the spot signal sent by the ground glass and transmit the spot signal to the measurement module of the DTOF camera.

[0012] Optionally, the laser intensity calibration module includes: a polarizer, an analyzer and an electro-optic modulator; The polarizer is arranged at the receiving end of the electro-optic modulator and connected to the transmitting end of the DTOF camera through a transmitting optical fiber, and is used for converting the initial laser into linearly polarized laser and sending it to the electro-optic modulator when receiving the initial laser emitted by the transmitting end; The electro-optic modulator is used to apply a modulation voltage to change the polarization state of the linearly polarized laser to generate modulated laser; The analyzer is arranged at the transmitting end of the electro-optic modulator and connected to the optical fiber switch through a transmitting optical fiber, and is used for detecting the polarization state of the modulated laser and transmitting the detected modulated laser back into the transmitting optical fiber; Wherein, the polarization transmission axes of the polarizer and the analyzer are perpendicular to each other, and the electro-optic modulator is arranged on the polarization transmission axis.

[0013] Optionally, the laser intensity calibration module further includes: a first lens and a second lens; The first lens is arranged at the connection between the polarizer and the transmitting optical fiber, and is used for collimating the initial laser onto the polarizer; The second lens is arranged at the connection between the analyzer and the transmitting optical fiber, and is used for converging the detected modulated laser into the transmitting optical fiber.

[0014] In a second aspect, an embodiment of the present invention provides a DTOF camera calibration method, which is applied to the above-mentioned DTOF camera calibration system based on a controllable delay optical fiber. The method includes: Coordinately control the delay optical fiber switching module, the laser intensity calibration module and the temperature calibration module to perform temperature calibration, depth calibration and intensity calibration in a preset order; In temperature calibration, by adjusting the ambient temperature and collecting depth images at multiple temperature points, fitting the relationship between temperature and ranging deviation, and obtaining a temperature compensation coefficient; In depth calibration, control the optical fiber switch to switch optical fiber branches of different lengths and collect corresponding depth images, and establish a mapping relationship between the measured value and the theoretical length through linear regression to obtain a depth calibration coefficient; In intensity calibration, dynamically adjust the laser intensity and collect depth images associated with the intensity, fit the relationship between intensity and ranging error, and obtain an intensity calibration coefficient; Write the temperature compensation coefficient, the depth calibration coefficient and the intensity calibration coefficient into the DTOF camera.

[0015] Optionally, by adjusting the ambient temperature and collecting depth images at multiple temperature points, fitting the relationship between temperature and ranging deviation, and obtaining a temperature compensation coefficient includes: After controlling the optical fiber switch to select an optical fiber branch with an optical path within the ranging range of the DTOF camera and controlling the laser intensity calibration module to apply the optimal modulation voltage that can be ranged by the DTOF camera, drive the temperature calibration module to change the ambient temperature of the transmitting end and the receiving end at a preset gradient; During the temperature change process, depth images collected by the DTOF camera are obtained at set temperature intervals, and the ranging mean value of all pixels in the depth image at each temperature is calculated; Based on the ranging mean value, the deviation amount between the actual ranging value of all pixels in the depth image at each temperature and the ranging mean value is calculated; Traverse all temperatures and the corresponding deviation amounts for polynomial curve fitting, and determine the polynomial coefficients of the obtained fitting curve as the temperature compensation coefficients.

[0016] Optionally, control the fiber optic switch to switch fiber optic branches of different lengths and collect the corresponding depth images, establish a mapping relationship between the measured value and the theoretical length through linear regression, and obtain the depth calibration coefficients including: After controlling the laser intensity calibration module to apply the optimal modulation voltage for the DTOF camera to range and the drive temperature calibration module to set the temperature of the DTOF camera to the optimal temperature state, control the fiber optic switch to sequentially switch fiber optic branches with increasing lengths until the preset ranging threshold is reached; Collect multiple frames of depth images under each fiber optic branch through the DTOF camera, and calculate the ranging mean value of pixels at the same position in all depth images under each fiber optic branch respectively to obtain the mean depth image; Traverse the ranging mean value of each pixel in the mean depth images belonging to all fiber optic branches and the theoretical ranging value belonging to the actual length of the fiber optic branch for linear fitting, and determine the fitting coefficients of the obtained fitting curve as the depth calibration coefficients.

[0017] Optionally, dynamically adjust the laser intensity and collect depth images associated with the intensity, fit the relationship between the intensity and the ranging error, and obtain the intensity calibration coefficients including: After controlling the fiber optic switch to select a fiber optic branch with an optical path within the ranging range of the DTOF camera and the drive temperature calibration module to set the temperature of the DTOF camera to the optimal temperature state, dynamically adjust the modulation voltage output by the laser intensity calibration module; Collect multiple frames of depth images at each intensity level through the DTOF camera, and calculate the ranging mean value and intensity mean value of pixels at the same position in all depth images at each intensity level respectively to obtain the mean depth image and the mean intensity image; Taking the mean depth image at the lowest intensity level as the reference, obtain the error depth image of the mean depth image at each intensity level and the mean depth image at the lowest intensity level; Traverse the ranging values and intensity values of pixels at the same position in the error depth images and the mean intensity images at all intensity levels for polynomial curve fitting, and determine the polynomial coefficients of the obtained fitting curve as the intensity calibration coefficients.

[0018] (III) Beneficial effects The beneficial effects of the present invention are: First, the present invention adopts an integrated calibration system, which integrates functions such as depth calibration, intensity calibration, and temperature calibration through a delay fiber switching module, a laser intensity calibration module, and a temperature calibration module, simplifies the calibration process, reduces calibration equipment and steps, and improves calibration efficiency.

[0019] Secondly, the delay fiber switching module in the present invention uses a fiber switch to switch fiber branches of different lengths, can precisely control the optical path, improves the calibration accuracy, and ensures the accuracy and reliability of the DTOF camera.

[0020] In addition, the present invention realizes automatic calibration and calibration through a control module, can adjust and optimize calibration parameters according to different measurement requirements and environmental changes, and enhances the flexibility and adaptability of the calibration system. Brief Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the composition of a DTOF camera calibration system based on a controllable delay fiber proposed in an embodiment of the present invention; Figure 2 It is a schematic diagram of the flow of a DTOF camera calibration method based on a controllable delay fiber proposed in an embodiment of the present invention;

Description of the Reference Signs

[0022] In order to better explain the present invention for easy understanding, the present invention will be described in detail below with reference to the accompanying drawings through specific embodiments.

[0023] Reference Figure 1As shown in the figure, a DTOF camera calibration system based on a controllable delay optical fiber proposed in an embodiment of the present invention includes: a delay optical fiber switching module, including an optical fiber switch 10 and a transmitting optical fiber and a receiving optical fiber 11 arranged on both sides of the optical fiber switch 10. The transmitting optical fiber is connected to the transmitting end of the DTOF camera. The receiving optical fiber 11 includes at least two optical fiber branches with different lengths and is connected to the receiving end of the DTOF camera. The optical fiber switch 10 is configured to switchably form an optical path between the transmitting optical fiber and any one of the optical fiber branches in the receiving optical fiber 11; a laser intensity calibration module, arranged on the transmitting optical fiber, for applying a modulation voltage to change the transmission characteristics of the laser transmitted in the transmitting optical fiber, so as to dynamically modulate the laser intensity of the DTOF camera; a temperature calibration module 16, arranged at the transmitting end and the receiving end, for changing the ambient temperature at the transmitting end and the receiving end, so as to perform temperature calibration on the DTOF camera; a control module 17, respectively connected to the optical fiber switch 10, the laser intensity calibration module, and the temperature calibration module 16, for controlling the optical fiber switch 10, the laser intensity calibration module, and the temperature calibration module 16 to form a multi-modal calibration environment.

[0024] In this embodiment, an integrated calibration system is adopted. By integrating functions such as depth calibration, intensity calibration, and temperature calibration through a delay optical fiber switching module, a laser intensity calibration module, and a temperature calibration module 16, the calibration process is simplified, the calibration equipment and steps are reduced, and the calibration efficiency is improved. At the same time, in the delay optical fiber switching module of this embodiment, the optical fiber switch 10 is used to switch optical fiber branches of different lengths, which can accurately control the optical path, improve the calibration accuracy, and ensure the accuracy and reliability of the DTOF camera. Moreover, in this embodiment, the control module 17 realizes automatic calibration and calibration, and can adjust and optimize the calibration parameters according to different measurement requirements and environmental changes, enhancing the flexibility and adaptability of the calibration system.

[0025] To better understand the above technical solutions, the exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more clear and thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0026] Specifically, referring to Figure 1 As shown in the figure, an embodiment of the present invention proposes a DTOF camera calibration system based on a controllable delay optical fiber, which includes: a delay optical fiber switching module, a laser intensity calibration module, a temperature calibration module 16, and a control module 17.

[0027] First, the delay optical fiber switching module includes: an optical fiber switch 10, and a transmitting optical fiber and a receiving optical fiber 11 disposed on both sides of the optical fiber switch 10. The transmitting optical fiber is connected to the transmitting end of the DTOF camera. The receiving optical fiber 11 includes at least two optical fiber branches with different lengths and is connected to the receiving end of the DTOF camera. The optical fiber switch 10 is configured to switchably form an optical path between the transmitting optical fiber and any one of the optical fiber branches in the receiving optical fiber 11.

[0028] In this embodiment, the receiving optical fiber 11 includes at least two optical fiber branches with a length difference of (L 1… L n ), which is positively correlated with the set target delay amount; the end of the optical fiber branch is provided with an optical fiber interface for pluggable connection to the receiving end. The optical fiber switch 10 has multiple input ends and output ends. The input ends are connected to the transmitting optical fiber, and one output end is connected to one optical fiber branch. The optical fiber switch 10 selects different optical fiber paths by switching the connection relationship between the input ends and the output ends. By selecting different optical fiber branches, the optical path of the laser can be changed, thereby realizing the calibration of different optical paths of the DTOF camera. Specifically, the measurement module 15 in the receiving end of the DTOF camera calculates the flight time of the laser in different optical fiber paths (the time difference between the emission and reception of the laser), and then obtains the optical path of the laser and the distance information of the object. Among them, all the input ends of the optical fiber switch 10 can be connected to the transmitting ends of the corresponding number of DTOF cameras through the transmitting optical fiber to realize the synchronous calibration work of multiple DTOF cameras.

[0029] In this embodiment, the transmitting end of the DTOF camera includes: a laser light source 1 and a first collimating mirror 2. The laser light source 1 is used to generate the transmitted laser; the first collimating mirror 2 is connected to the transmitting optical fiber and is used to collimate the transmitted laser into the transmitting optical fiber.

[0030] In this embodiment, the receiving end of the DTOF camera includes: a second collimating mirror 12, a ground glass 13, and a receiving lens 14. The second collimating mirror 12 is connected to the receiving optical fiber 11 and is used to collimate the laser transmitted in the receiving optical fiber 11 into parallel laser; the ground glass 13 is used to scatter the parallel laser into a uniformly distributed spot signal; the receiving lens 14 is used to transmit the spot signal to the measurement module 15 of the DTOF camera after receiving the spot signal sent by the ground glass 13.

[0031] Secondly, the laser intensity calibration module is disposed on the transmitting optical fiber and is used to apply a modulation voltage to change the transmission characteristics of the laser transmitted in the transmitting optical fiber to dynamically modulate the laser intensity of the DTOF camera. The laser intensity calibration module includes: a polarizer 5, an analyzer 7, an electro-optic modulator 6, a first lens 4, and a second lens 8.

[0032] In this embodiment, the polarizer 5 is arranged at the receiving end of the electro-optic modulator 6 and is connected to the transmitting end of the DTOF camera through a transmitting optical fiber (the first transmitting optical fiber 3). When receiving the initial laser emitted by the transmitting end, the polarizer 5 is used to convert the initial laser into linearly polarized laser and send it to the electro-optic modulator 6; the electro-optic modulator 6 is used to apply a modulation voltage to change the polarization state of the linearly polarized laser to generate modulated laser; the analyzer 7 is arranged at the transmitting end of the electro-optic modulator 6 and is connected to the optical fiber switch 10 through a transmitting optical fiber (the second transmitting optical fiber 9). The analyzer 7 is used to detect the polarization state of the modulated laser and send the detected modulated laser back to the transmitting optical fiber (the second transmitting optical fiber 9); the first lens 4 is arranged at the connection between the polarizer 5 and the transmitting optical fiber and is used to collimate the initial laser onto the polarizer 5; the second lens 8 is arranged at the connection between the analyzer 7 and the transmitting optical fiber and is used to converge the detected modulated laser into the transmitting optical fiber. Among them, the polarization-transmitting axes of the analyzer 7 and the polarizer 5 are perpendicular to each other, and the electro-optic modulator 6 is arranged on the polarization-transmitting axis.

[0033] Next, the temperature calibration module 16 is arranged at the transmitting end and the receiving end of the DTOF camera and is used to change the ambient temperature of the transmitting end and the receiving end to calibrate the temperature of the DTOF camera.

[0034] In this embodiment, the temperature calibration module 16 selects a thermoelectric cooler. The thermoelectric cooler can heat or cool the transmitting end (i.e., the laser light source 1 and its related components) and the receiving end (i.e., the receiving lens 14 and its related components) according to the instructions of the control module 17, so as to accurately control their ambient temperature. Through temperature control, the measurement error caused by temperature change can be further reduced, and the stability and accuracy of the DTOF camera can be improved.

[0035] Finally, the control module 17 is respectively connected to the optical fiber switch 10, the laser intensity calibration module, and the temperature calibration module 16, and is used to control the optical fiber switch 10, the laser intensity calibration module, and the temperature calibration module 16 to form a multi-modal calibration environment.

[0036] In this embodiment, the control module 17 can cooperate to control the delay optical fiber switching module, the laser intensity calibration module, and the temperature calibration module 16, perform temperature calibration, depth calibration, and intensity calibration in a preset order, and write multi-dimensional calibration parameters such as temperature compensation coefficients, depth calibration coefficients, and intensity calibration coefficients obtained during the calibration process into the DTOF camera, and then complete the calibration work of the DTOF camera.

[0037] In addition, as shown in Figure 2 Furthermore, the embodiment of the present invention also proposes a DTOF camera calibration method. The calibration method is applied to the above-mentioned DTOF camera calibration system based on a controllable delay optical fiber. Its execution subject is the control module 17, and the method includes: S100, the collaborative control delay optical fiber switching module, the laser intensity calibration module, and the temperature calibration module 16 perform temperature calibration, depth calibration, and intensity calibration in a preset order.

[0038] S200a. In temperature calibration, by adjusting the ambient temperature and collecting depth images at multiple temperature points, fitting the relationship between temperature and ranging deviation, and obtaining the temperature compensation coefficient.

[0039] S200b. In depth calibration, control the fiber optic switch 10 to switch fiber optic branches of different lengths and collect corresponding depth images, establish a mapping relationship between the measured value and the theoretical length through linear regression, and obtain the depth calibration coefficient.

[0040] S200c. In intensity calibration, dynamically adjust the laser intensity and collect depth images associated with the intensity, fit the relationship between intensity and ranging error, and obtain the intensity calibration coefficient.

[0041] S300. Write the temperature compensation coefficient, the depth calibration coefficient, and the intensity calibration coefficient into the DTOF camera.

[0042] In this embodiment, step S200a may include the following sub-steps S210a to S240a: S210a. After controlling the fiber optic switch 10 to select a fiber optic branch with an optical path within the ranging range of the DTOF camera and controlling the laser intensity calibration module to apply the optimal modulation voltage for ranging of the DTOF camera, drive the temperature calibration module 16 to change the ambient temperature of the transmitting end and the receiving end at a preset gradient.

[0043] Control the fiber optic switch 10 to select a fiber optic branch with an optical path within the DTOF ranging range to ensure that the optical path is always within the ranging range of the DTOF camera during the temperature change process.

[0044] S220a. During the temperature change process, obtain the depth images collected by the DTOF camera at a set temperature interval, and calculate the ranging mean value of all pixels in the depth image at each temperature.

[0045] For example, within the set temperature range (-20°C to 60°C), record a depth image every 0.5°C, and statistically calculate the ranging mean value of all pixels in the depth image at each temperature as the reference value for the current temperature change, which is used to calculate the deviation amount between the ranging of each pixel at each temperature and the reference value.

[0046] S230a. Based on the ranging mean value, calculate the deviation amount between the actual ranging value and the ranging mean value of all pixels in the depth image at each temperature.

[0047] S240a. Traverse all temperatures and the corresponding deviation amounts for polynomial curve fitting, and determine the polynomial coefficients of the obtained fitting curve as the temperature compensation coefficient.

[0048] In this embodiment, step S200b may include the following sub-steps S210b to S230b: S210b. After controlling the laser intensity calibration module to apply the optimal modulation voltage for distance measurement of the DTOF camera and driving the temperature calibration module 16 to set the temperature of the DTOF camera to the optimal temperature state, control the optical fiber switch 10 to sequentially switch the optical fiber branches with increasing lengths until the preset distance measurement threshold is reached.

[0049] For example, when the optical fiber switch 10 sequentially switches the optical fiber branches with increasing lengths until the preset distance measurement threshold is reached, the range can be 0.1m to 15m.

[0050] S220b. Collect multiple frames of depth images under each optical fiber branch through the DTOF camera, and respectively calculate the distance measurement mean values of the pixels at the same position in all depth images under each optical fiber branch to obtain the mean depth image. S230b. Traverse the distance measurement mean values of each pixel in the mean depth images belonging to all optical fiber branches and perform linear fitting with the theoretical distance measurement values corresponding to the actual lengths of the optical fiber branches, and determine the fitting coefficient of the obtained fitting curve as the depth calibration coefficient.

[0051] For each pixel in the depth image, the depth image acquired by each optical path obtains the corresponding pixel measurement as x and the theoretical distance measurement as D, and several groups of {x, D} can be obtained. Use linear fitting to calculate the corresponding relationship between x and D, and its fitting coefficient is the depth calibration coefficient.

[0052] In this embodiment, step S200c may include the following sub-steps S210c to S240c: S210c. After controlling the optical fiber switch 10 to select the optical fiber branch whose optical path is within the distance measurement range of the DTOF camera and driving the temperature calibration module 16 to set the temperature of the DTOF camera to the optimal temperature state, dynamically adjust the modulation voltage output by the laser intensity calibration module.

[0053] S220c. Collect multiple frames of depth images at each intensity level through the DTOF camera, and respectively calculate the distance measurement mean values and intensity mean values of the pixels at the same position in all depth images at each intensity level to obtain the mean depth image and the mean intensity image.

[0054] The intensity change range is determined according to the modulation voltage, and its intensity value is proportional to the modulation voltage. For example: when the modulation voltage is 0V, the corresponding intensity value is 1; when the modulation voltage is 12V, the corresponding intensity value is 0.5; when the modulation voltage is 24V, the corresponding intensity value is 0.

[0055] S230c. Taking the mean depth image at the lowest intensity level as a reference, obtain the error depth image of the mean depth image at each intensity level and the mean depth image at the lowest intensity level.

[0056] S240c. Traverse the ranging values and intensity values of the pixels at the same position in the error depth images and mean intensity images at all intensity levels for polynomial curve fitting, and determine the polynomial coefficients of the obtained fitting curve as the intensity calibration coefficients.

[0057] In summary, a DTOF camera calibration system and method based on a controllable delay optical fiber are proposed in this embodiment. First, through an integrated calibration system, functions such as intensity calibration, optical path calibration, and temperature calibration are integrated together to achieve multi-dimensional parameter calibration of the DTOF camera, and the calibration process is also simplified, reducing calibration equipment and steps and improving calibration efficiency. Second, components such as a high-precision laser light source 1, a collimating mirror, an electro-optic modulator 6, an optical fiber switch 10, a temperature calibration module 16, and a measurement module 15 are used to perform multi-dimensional parameter calibration by precisely controlling the laser intensity, optical path, and ambient temperature, improving the calibration accuracy and ensuring the accuracy and reliability of the DTOF camera. Also, through the control module 17, automatic calibration and calibration can be realized, and adjustments and optimizations can be made according to different measurement requirements and environmental changes, enhancing the flexibility and adaptability of the system.

[0058] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0059] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams can be implemented by computer program instructions, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can also be implemented by computer program instructions.

[0060] It should be noted that in the description of the present invention, the words "a" or "an" preceding a component do not exclude the existence of multiple such components. The present invention can be implemented by means of hardware including several different components and by means of a suitably programmed computer. The use of the words first, second, third, etc. is only for the convenience of expression and does not represent any order. These words can be understood as part of the component name.

[0061] In addition, it should be noted that in the description of this specification, the descriptions of terms such as "one embodiment", "some embodiments", "embodiment", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0062] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments after learning the basic creative concept.

[0063] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention.

Claims

1. A DTOF camera calibration system based on a controllable delay optical fiber, characterized in that, Comprising: A delay optical fiber switching module, including an optical fiber switch and a transmitting optical fiber and a receiving optical fiber arranged on both sides of the optical fiber switch. The transmitting optical fiber is connected to the transmitting end of the DTOF camera. The receiving optical fiber includes at least two optical fiber branches with different lengths and is connected to the receiving end of the DTOF camera. The optical fiber switch is configured to switchably form an optical path between the transmitting optical fiber and any one of the optical fiber branches in the receiving optical fiber; A laser intensity calibration module, arranged on the transmitting optical fiber, for applying a modulation voltage to change the transmission characteristics of the laser transmitted in the transmitting optical fiber, so as to dynamically modulate the laser intensity of the DTOF camera; A temperature calibration module, arranged at the transmitting end and the receiving end, for changing the ambient temperature of the transmitting end and the receiving end, so as to perform temperature calibration on the DTOF camera; A control module, respectively connected to the optical fiber switch, the laser intensity calibration module and the temperature calibration module, for controlling the optical fiber switch, the laser intensity calibration module and the temperature calibration module to form a multi-modal calibration environment.

2. The DTOF camera calibration system according to claim 1, characterized in that, The receiving optical fiber includes at least two optical fiber branches with a length difference of which is positively correlated with a set target delay amount; An optical fiber interface is arranged at the end of the optical fiber branch, and the optical fiber interface is used for pluggable connection with the receiving end.

3. The DTOF camera calibration system according to claim 1, wherein The transmitting end includes: a laser light source and a first collimating mirror; The laser light source is used for generating transmitted laser; The first collimating mirror is connected to the transmitting optical fiber and is used for collimating the transmitted laser into the transmitting optical fiber.

4. The DTOF camera calibration system according to claim 1, characterized in that, The receiving end includes: A second collimating mirror, a ground glass and a receiving lens; The second collimating mirror is connected to the receiving optical fiber and is used for collimating the laser transmitted in the receiving optical fiber into parallel laser; The ground glass is used for scattering the parallel laser into a uniformly distributed spot signal; The receiving lens is used for receiving the spot signal sent by the ground glass and transmitting the spot signal to the measurement module of the DTOF camera.

5. The DTOF camera calibration system according to claim 1, wherein, The laser intensity calibration module includes: a polarizer, an analyzer and an electro-optic modulator; The polarizer is arranged at the receiving end of the electro-optic modulator and is connected to the transmitting end of the DTOF camera through the transmitting optical fiber. When receiving the initial laser emitted by the transmitting end, the polarizer is used for converting the initial laser into linearly polarized laser and sending it to the electro-optic modulator; The electro-optic modulator is used for applying a modulation voltage to change the polarization state of the linearly polarized laser to generate modulated laser; The analyzer is arranged at the sending end of the electro-optic modulator and is connected to the optical fiber switch through the transmitting optical fiber. The analyzer is used for detecting the polarization state of the modulated laser and transmitting the detected modulated laser back into the transmitting optical fiber; Wherein, the polarization transmission axes of the polarizer and the analyzer are perpendicular to each other, and the electro-optic modulator is arranged on the polarization transmission axis.

6. The DTOF camera calibration system according to claim 5, characterized in that, The laser intensity calibration module further includes: a first lens and a second lens; The first lens is arranged at the connection between the polarizer and the transmitting optical fiber and is used for collimating the initial laser onto the polarizer; The second lens is arranged at the connection between the analyzer and the transmitting optical fiber and is used for converging the detected modulated laser into the transmitting optical fiber.

7. A DTOF camera calibration method, characterized in that, The method is applied to the DTOF camera calibration system based on a controllable delay optical fiber according to any one of claims 1-6 above. The method includes: Cooperatively controlling the delay optical fiber switching module, the laser intensity calibration module and the temperature calibration module to perform temperature calibration, depth calibration and intensity calibration in a preset order; In temperature calibration, by adjusting the ambient temperature and collecting depth images at multiple temperature points, fitting the relationship between temperature and ranging deviation, the temperature compensation coefficient is obtained; In depth calibration, control the fiber optic switch to switch fiber optic branches of different lengths and collect corresponding depth images, establish the mapping relationship between the measured value and the theoretical length through linear regression, and obtain the depth calibration coefficient; In intensity calibration, dynamically adjust the laser intensity and collect depth images related to intensity, fit the relationship between intensity and ranging error, and obtain the intensity calibration coefficient; Write the temperature compensation coefficient, depth calibration coefficient, and intensity calibration coefficient into the DTOF camera.

8. The DTOF camera calibration method according to claim 7, wherein By adjusting the ambient temperature and collecting depth images at multiple temperature points, fitting the relationship between temperature and ranging deviation, obtaining the temperature compensation coefficient includes: After controlling the fiber optic switch to select a fiber optic branch with an optical path within the ranging range of the DTOF camera and controlling the laser intensity calibration module to apply the optimal modulation voltage for ranging of the DTOF camera, drive the temperature calibration module to change the ambient temperature of the transmitter and receiver at a preset gradient; During the temperature change process, obtain the depth images collected by the DTOF camera at a set temperature interval, and calculate the ranging mean value of all pixels in the depth image at each temperature; Based on the ranging mean value, calculate the deviation amount between the actual ranging value and the ranging mean value of all pixels in the depth image at each temperature; Traverse all temperatures and the corresponding deviation amounts for polynomial curve fitting, and determine the polynomial coefficients of the obtained fitting curve as the temperature compensation coefficient.

9. The DTOF camera calibration method according to claim 7, wherein, Control the fiber optic switch to switch fiber optic branches of different lengths and collect corresponding depth images, establish the mapping relationship between the measured value and the theoretical length through linear regression, obtaining the depth calibration coefficient includes: After controlling the laser intensity calibration module to apply the optimal modulation voltage for ranging of the DTOF camera and driving the temperature calibration module to set the temperature of the DTOF camera to the optimal temperature state, control the fiber optic switch to sequentially switch fiber optic branches with increasing length until the preset ranging threshold is reached; Collect multiple frames of depth images under each fiber optic branch through the DTOF camera, and calculate the ranging mean value of the same-position pixels in all depth images under each fiber optic branch respectively to obtain the mean depth image; Traverse the ranging mean value of each pixel in the mean depth images belonging to all fiber optic branches and the theoretical ranging value belonging to the actual length of the fiber optic branch for linear fitting, and determine the fitting coefficient of the obtained fitting curve as the depth calibration coefficient.

10. The DTOF camera calibration method according to claim 7, wherein Dynamically adjust the laser intensity and collect depth images related to intensity, fit the relationship between intensity and ranging error, obtaining the intensity calibration coefficient includes: After controlling the fiber optic switch to select a fiber optic branch with an optical path within the ranging range of the DTOF camera and driving the temperature calibration module to set the temperature of the DTOF camera to the optimal temperature state, dynamically adjust the modulation voltage output by the laser intensity calibration module; Collect multiple frames of depth images at each intensity level through the DTOF camera, and calculate the ranging mean value and intensity mean value of the same-position pixels in all depth images at each intensity level respectively to obtain the mean depth image and mean intensity image; Based on the mean depth image at the lowest intensity level, obtain the error depth image of the mean depth image at each intensity level and the mean depth image at the lowest intensity level; Traverse the ranging values and intensity values of the pixels at the same position in the error depth image and the mean intensity image at all intensity levels for polynomial curve fitting, and determine the polynomial coefficients of the obtained fitting curve as the intensity calibration coefficients.

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